The invention concerns a method to sharpen the cutting knife of a knife ring chipper. This includes specifically knife ring chippers to process wood into wood chips for further industrial processing, such as raw material for chipboards.
Such chippers have a knife ring, which supports a number of knife units. The knife units are arranged such that the cutting edges of the knives run parallel to the axis of the knife ring. Each unit contains a cutting knife, which extends with its cutting edge to the inside, and a holder plate, to which the knife is attached by a screw.
A rotor rotates in the interior space between the knives. A supply of wood particles is introduced into the interior space, to be thrown against the cutting edges of the knives by the rotor.
The desired chip size is determined by the distance of the knife from the so-called wearing plates, which are, in turn, also a component of the knife ring.
The relatively short useful life of the cutting knives is a major problem. They may be worn out within a few hours and can no longer supply chips of the required quality. The exchange of knives requires a particularly high labor input.
Consequently, efforts have been expended for a long time to improve the exchange of the knives. Thus, one method is known, which includes the following processing steps:
First, the knife basket is removed from the chipper and placed in a sharpening apparatus. The knife basket can be rotated around its own axis in this sharpening apparatus. The dull knives are removed from their holders and are placed n the holder for sharpening the knives at the proper working depth. The knives are then sharpened and are subsequently reinserted in the knife basket. The sharpening process uses grinding tool that includes one or several grinding disks. The grinding tool moves parallel t the axis of the knife bodies. If the tool uses several grinding disks, they are arranged side-by-side and are all used simultaneously. The knife ring is turned after each grinding operation , until all knives have been sharpened.
Admittedly, machines of this type have shown their value. However, the construction cost is high, and this inflates the production cost of chip material. In addition, the machine can be operated efficiently only if there is no breakdown and with only a limited number of knife types.
The invention is focused on the objective of developing a method that allows for flawless, fast and efficient sharpening of the dulled knives and which also fulfills the technological requirements for the quality of chipping, even if operation does not run flawlessly. In addition, it should also allow for efficient sharpening of knives of several different knife ring types. Finally, the production costs of the final hipped material should be as low as possible.
The essential steps of the method according to the invention are the following:
First remove the knife ring from the knife ring chipper. Then disassemble the knife units, which means that the individual knife is removed from its holder plate and sharpened.
The intermediate storage of the dull and sharpened knives in separate buffer stations is an important step in this method. This has the advantage that the sharpening process can be decoupled from the assembly process, which decreases the cycle time. Cycle time is defined as the time from input of the dull knife unit until ejection of the sharpened knife unit from the system. This method of disassembly and assembly of the knife unit has the additional advantage that the resin deposits between knife and holding plate can be removed by cleaning after disassembly and that the cutting knives may be selected out and replaced, depending on their degree of wear.
The dull knives are inserted in a grinding unit, which grinds off a pre-specified amount or which can determine the amount of grinding independently based upon a measurement of wear. However, the grinding process may also be realized by other chip-removal, thermal or physical-chemical methods. While the grinding of each individual knife requires extra time, it provides for the possibility of individual grinding specifications. This has the advantage that the knives are used for longer periods in production, before they are rejected for insufficient knife width. Thus, the operating hours per knife are increased significantly. Given approximately 60 cutting knives in each knife ring, this generates a reduction of the costs for each knife ring. The holding plate is not replaced during the entire process and is moved online through the processing line. Exceptions relate to very significantly worn holding plates, which are replaced by the user manually.
This method allows the user to specify and set the knife cutting depth individually for each knife ring. Also, the holding plate from each knife ring is re-used in that same ring. This is important for the function of the knife ring.
The knives are held in a certain angle in the buffer station in order to avoid potential contact among the knives. The angle modifies the center of gravity of the knives such that safe stacking of knives with varying width is possible.
An adjustment unit receives the knife units via pre-selected input points, which vary according to knife type and which may be adapted to the knife unit. This has the advantage that any type of knife unit may be processed in the system with minimal change-over, which provides maximum flexibility for the user. It is also possible to work on units consisting of several components.
The holding plate is firmly held on a mounting base throughout the assembly process. The very precise movement of the mounting base allows for high adjustment precision of the knife depth.
It is most advantageous to use chain holders, which have a high volume with low space requirements, for storage of the incoming or ejected knife units.